ARM: 5874/1: serial21285: fix disable_irq-from-interrupt-handler deadlock

The console hangs during bootup when disable_irq is called from the
transmit interrupt handler (it will wait forever for it's "own"
interrupt in synchronize_irq). Fix by using disable_irq_nosync()
instead.

Signed-off-by: Simon Kagstrom <simon.kagstrom@netinsight.net>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>