input: sensors: fix MPU6050 sample rate issue

MPU6050 hardware sample rate is fixed at 50Hz in polling mode, driver
cannot get enough number of new samples and fail on sensor frequency
check.

CRs-fixed: 736320
Change-Id: I5b2dfceda19639a97176232d0aba8f7c0c4e88e4
Signed-off-by: Bingzhe Cai <bingzhec@codeaurora.org>