TWL4030: change init-time IMR mask code to WARN if error

TWL4030: change init-time IMR mask code to WARN if error

twl_init_irq() prints error messages and returns if any interrupt mask
register writes fail.  Change this to generate a warning traceback and
to continue execution rather than skipping TWL init.  (These mask
writes should not fail at all unless either the I2C bus or the TWL4030
is somehow wedged.)

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>