irqchip/stm32-exti: Fix minor indentation issue

Commit 046a6ee2 ("irqchip: Bulk conversion to
generic_handle_domain_irq()") incorrectly added a leading space character
in the line indentation.

Use only TAB for indentation, removing the leading space.

Signed-off-by: Antonio Borneo <antonio.borneo@foss.st.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240415134926.1254428-2-antonio.borneo@foss.st.com