wil6210: Set default 3-MSI

Single MSI is the current default configuration.
With multiple MSI interrupts configuration, Tx/Rx processing could
run in parallel on different CPU cores and allow better balance
between the cores.

Change-Id: I2143d22f355c5c1f853801973c969be58e6535d5
Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>