LimeRFE: fix crash when changing TX/RX mode over I2C
LimeRFE: fix crash when changing TX/RX mode over I2C

use buffer size parameter in i2c_read_buffer() instead of RFE_BUFFER_SIZE define
Cmd_Mode() uses smaller buffer size than RFE_BUFFER_SIZE

myriadrf/LimeSuite,limemicro/lms7suite,limemicro/lms7suite,myriadrf/LimeSuite,limemicro/lms7suite,myriadrf/LimeSuite,limemicro/lms7suite,limemicro/lms7suite,myriadrf/LimeSuite,myriadrf/LimeSuite