serial: msm_geni_serial: use correct API to free memory

Uart driver uses devm* callback to allocate memory but
uses non devm* callback to free the same allocated memory.
This leads to memory leak.

Use the right callback to free memory.

Change-Id: Ia80603d09bf7a59fc2e0467ca33df0a618eabe4e
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>