ARM: 8450/1: v7-M: Use ret_to_user_from_irq in PendSV handler

The PendSV handler calls v7m_exception_entry which
disables IRQs. Therefore, since IRQs are already disabled,
the PendSV handler can return using ret_to_user_from_irq.

Signed-off-by: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>