serial: msm_geni_serial: Modify the Rx state machine abort sequence

When issuing the abort to the Rx state machine poll the command control
register bit instead of the interrupt bit as this is more reliable during
bootup.

Change-Id: Ie30c581fa2e97c63f9c2b247eabb2d21c11e8cd2
Signed-off-by: Girish Mahadevan <girishm@codeaurora.org>