wifi: wl18xx: make wl18xx_tx_immediate_complete() more efficient

wifi: wl18xx: make wl18xx_tx_immediate_complete() more efficient

wl18xx_tx_immediate_complete() iterates through the completed transmit
descriptors in a circular fashion, and in doing so uses a modulus
operation that is not a power of two. This leads to inefficient code
generation, which can be easily solved by providing a helper to
increment to the next descriptor. Use this more efficient solution.

Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/E1sBsxn-00E8vW-9h@rmk-PC.armlinux.org.uk