Incorrect SRAM size for L496x and L4A6x

[AMillerNV]

stlink/config/chips/L496x_L4A6x.chip

Line 9 in c2db68e

sram_size 0x40000 // 256 KB

Should be 0x50000 for these devices

[Nightwalker-87]

Will be fixed soon. Thanks for reporting.