dt-bindings: mfd: iqs62x: Do not override firmware-name $ref

dtschema package defines firmware-name as string-array, so individual
bindings should not make it a string but instead just narrow the number
of expected firmware file names.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Jeff LaBundy <jeff@labundy.com>
Link: https://lore.kernel.org/r/20240115182042.1610134-1-krzysztof.kozlowski@linaro.org


Signed-off-by: Lee Jones <lee@kernel.org>