iio: magnetometer: rm3100: add boundary check for the value read from RM3100_REG_TMRC

In the Linux kernel, the following vulnerability has been resolved:

iio: magnetometer: rm3100: add boundary check for the value read from RM3100_REG_TMRC

Recently, we encounter kernel crash in function rm3100_common_probe

caused by out of bound access of array rm3100_samp_rates (because of

underlying hardware failures). Add boundary check to prevent out of

bound access.