pinctrl: renesas: r8a779g0: Fix CANFD5 suffix

CAN-FD instance 5 has two alternate pin groups: "canfd5" and "canfd5_b".
Rename the former to "canfd5_a" to increase uniformity.

While at it, remove the unneeded separator.

Fixes: ad9bb2fe ("pinctrl: renesas: Initial R8A779G0 (R-Car V4H) PFC support")
Fixes: 050442ae ("pinctrl: renesas: r8a779g0: Add pins, groups and functions")
Fixes: c2b4b2cd ("pinctrl: renesas: r8a779g0: Add missing CANFD5_B")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/10b22d54086ed11cdfeb0004583029ccf249bdb9.1717754960.git.geert+renesas@glider.be