extEEPROM::read() fix error and make it debuggable

[dwrobel]

Fixes the follwing compilation errors on the STM32 platform:

extEEPROM/extEEPROM.cpp: In member function 'byte extEEPROM::read(long unsigned int, byte*, unsigned int)':
extEEPROM/extEEPROM.cpp:185:51: error: ISO C++ says that these are ambiguous, even though the worst conversion for the first is better than the worst conversion for the second: [-Werror]
communication->requestFrom(ctrlByte, nRead);
^
In file included from extEEPROM/extEEPROM.h:62,
from extEEPROM/extEEPROM.cpp:58:
STM32/hardware/stm32/1.6.0-dev/libraries/Wire/src/Wire.h:98:13: note: candidate 1: 'uint8_t TwoWire::requestFrom(int, int)'
uint8_t requestFrom(int, int);
^~~~~~~~~~~
STM32/hardware/stm32/1.6.0-dev/libraries/Wire/src/Wire.h:95:13: note: candidate 2: 'uint8_t TwoWire::requestFrom(uint8_t, uint8_t)'
uint8_t requestFrom(uint8_t, uint8_t);
^~~~~~~~~~~
cc1plus: all warnings being treated as errors
Using library extEEPROM at version 3.4.1 in folder: extEEPROM
Using library Wire at version 1.0 in folder: .arduino15/packages/STM32/hardware/stm32/1.6.0-dev/libraries/Wire
exit status 1
make: *** [makefile.stm32:67: build] Error 1

Tested using: https://github.com/stm32duino/Arduino_Core_STM32

Also:

• Modernize the read() method to use 'const' where the variable
  is not modified after assignment.
• Remove C-like casts and use C++ static_cast<>.
• Make the code debuggable, by moving 'return' statements to a
  separate line, as on STM32 platform debugger is widely available.