clk: at91: sam9x7: Remove gmac peripheral clock with ID 67

clk: at91: sam9x7: Remove gmac peripheral clock with ID 67

According with datasheet (see link section) table 12.1 the instance ID 67
is reserved. This change drops the gmactsu_clk entry from the SAM9X7 clock
description table to align with the datasheet.

Link: https://ww1.microchip.com/downloads/aemDocuments/documents/MPU32/ProductDocuments/DataSheets/SAM9X7-Series-Data-Sheet-DS60001813.pdf
Signed-off-by: Mihai Sain <mihai.sain@microchip.com>
Link: https://lore.kernel.org/r/20260309075329.1528-2-mihai.sain@microchip.com
[claudiu.beznea: massaged the patch description]
Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>