Fixes the following Coverity warning:
** CID 1539495: Integer handling issues (CONSTANT_EXPRESSION_RESULT)
/bsps/shared/dev/rtc/mcp7940m.c: 317 in mcp7940m_set_time()
Basically coverity warns that (buf[...] & 0x7) can't be bigger than 7.
Just remove the unnecessary comparison.
The MCP7940M is a I2C RTC chip. The new driver uses the dev/i2c API to
support the RTC. It is written with the intention, that the driver can
be adapted to other RTCs with a similar register layout by just
replacing the initialization function.