NFC: st21nfca: Get rid of "interesting" use of interrupt polarity

I2C framework followed by IRQ framework does set interrupt polarity
correctly if it's properly specified in firmware (ACPI or DT).

Get rid of the redundant trick when requesting interrupt.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Samuel Ortiz <sameo@linux.intel.com>