input: synaptics_i2c_rmi4: remove deprecated apis in 3.18 kernel

usleep is deprecated in 3.18 kernel and hence replace it with
usleep_range. Also, add flags parameters to the function call
of input_mt_init_slots.

Change-Id: I387b84d80048e9e7720360db3c67df235c401c3b
Signed-off-by: Abinaya P <abinayap@codeaurora.org>